Electroluminescent device



DecQlS, 1962 D. BERG ETAL 3,069,579

ELECTROLUMINESCENT DEVICE Filed March 18, 1960 FIG. I.

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vania Filed Mar. 18, 1960, Ser. No. 15,857 13 Claims. (Cl. 313108) Thisinvention relates to electroluminescent devices and, more particularly,to flexible electroluminescent devices which can be readily conformedinto any desired shape and electroluminescent devices which have asubstantially uniform light output.

The phenomenon of electroluminescence was first comprehensivelydisclosed by G. Destriau, one of his earlier publications appearing inLondon, Edinburgh and Dublin Philosophical Magazine, Series 7, vol. 38,No. 285, pages 700737 (October 1947). Since this early publication,electroluminescent devices have been marketed commercially.

Most electroluminescent devices are rigid in nature andare not adaptedto be conformed into different shapes. Also, thelight emitted byelectroluminescent devices often varies in intensity because ofvariations in electrode spacing.

It is the general object of this invention to provide a flexibleelectroluminescent device which can be readily conformed to variousshapes.

It is another objectto provide an electroluminescent device which emitsa very uniform light intensity.

It is a further object to provide constructional details for suchflexible or uniform-appearing electroluminescent devices.

It is an additional object to provide light-transmitting, flexible andconducting solid substance.

The aforesaid objects of the invention, and other objects which willbecome apparent as the description proceeds, are achieved by providing aflexible electroluminescent device wherein a flexible, conducting coresuch as a wire has carried thereon a flexible layer comprisingelectroluminescent phosphor. Over the phosphor layer is carried aflexible, light-transmitting, electricallyconducting and solid layer.This electroluminescent structure in essence has the appearance of awire and it is readily conformed into various shapes. There is alsoprovided an electroluminescent device which emits light ofsubstantially-uniform intensity by virtue of at least one additionallayer of flexible, light-transmitting, electricallyconducting and solidmaterial included between a lighttransmitting electrode and the phosphorof the device. This additional layer compensates for variations inelectrode spacing, as are frequently encountered with electroluminescentdevices.

For a better understanding of the invention, reference should be had tothe accompanying drawings wherein:

FIG. 1 is an elevational view, partly in section, of a flexibleelectroluminescent device constructed in accordance with this invention;

FIG. 2 is a cross-sectional view taken on the line IIII in FIG. 1, inthe direction of the arrows;

FIG. 3 illustrates a practical application for the device as shown inFIG. 1;

FIG. 4 is an elevational view, partly in section, of an alternativeconstruction for the device as shown in FIG.

3,069,579 Patented Dec. 18, 1962 1, wherein an additional bus bar isembedded in the flexible, light-transmitting and solid electrode layer;

FIG. 5 is a cross-sectional view taken on the line V-V in FIG. 4;

FIG. 6 is a fragmentary perspective view of an electroluminescent deviceadapted to emit light from opposite faces and wherein additional layersof flexible, lighttransmitting, electrically-conducting and solidmaterial are also included between the device electrodes, so that theemitted light is of substantially uniform intensity.

FIG. 7 is a fragmentary perspective view of an alternative embodimentfor the device as shown in FIG. 6.

With specific reference to the form of the invention illustrated in thedrawings, the device 10 as shown in FIGS. 1 and 2 generally comprises aflexible metallic body 12 carrying thereon a flexible layer 14comprising electroluminescent phosphor. Over the phosphor layer 14 iscarried a flexible, light-transmitting, electricallyconducting and solidlayer 16. As a specific example, the core 12 is formed of copper wirehaving a diameter of 64 mils. The layer 14 comprises anyelectroluminescent phosphor, an example being the well-known Zincsulfide activated by copper and coactivated by chlorine. Desirably,there is mixed with the phosphor a light-transmitting dielectricmaterial such as an epoxy-modified polyester varnish orpolyvinyl-chloride acetate. The relative parts by weight of phosphor anddielectric are not critical and equal parts by weight of phosphor anddielectric are satisfactory. The thickness of the layer .14 is notcritical and as an example is 2 mils. The layer 46 can be formed of anymaterial which is flexible, light transmitting, electrically conductingand solid. As a specific example, the layer 16 is formed of waxy solidssuch as succinonitrile (MP. 57 C.) or 2,2-dinitropropane (M.P. 53 C.) asbase material. To render these indicated materials electricallyconductive, there is dissolved in them a predetermined amount of anionizable organic or inorganic salt. Examples of suitable dissolvedsalts are ammonium chloride, potassium bromide, ammonium acetate, (CH=NCl or triethyl acetomethyl ammonium bromide (the triethyl quaternaryammonium bromide of glycinonitrile). These indicated materials can beadded in amount of from 0.03% to 2.5% by weight of the indicated basematerial and even this range can be extended. As a specific example,when 0.128 gram of triethyl acetomethyl ammonium bromide is dissolved in5.29 grams of succinonitrile the composite material will have aresistance in the order of 2500 ohms as measured across a /8 inchspacing. The succinonitrile for example displays a very high resistance,but when the foregoing inorganic or organic ionizable salts aredissolved therein, the resulting composite material becomes electricallyconducting in nature. It should be noted that the foregoing indicatedamounts of ionizable dissolved material are not meant to be limiting andother salts can be substituted for those indicated. Apparently thereason for the conductivity of these modified waxy solid materials isthat the dissolved electrolytes apparently form free ions which aremobile in the solid base material. The layer 16 preferably has aconsiderable thickness as compared to the phosphor layer 14, in order tofacilitate application and to minimize any tendency for overly-thincoating portions which could form discrete high resistance points. As anexample, the layer 16 has a thickness of 60 mils and this thickness issubject to considerable variation. As with other electroluminesrials canbe substituted therefor.

cent devices, the spaced electrodes of the device are adapted to have analternating potential applied therebetween. In the embodiment as shownin FIGS. 1 and 2, the copper core wire 12 extends beyond the coatingsthereon and a contacting sleeve 20 fits over this extending portion tofacilitate electrical connection. An additional contacting sleeve 22fits about the electrode layer 16 in order to facilitate electricalconnection to this electrode layer.

In FIG. 3 is shown a practical application for the electroluminescentwire as shown in FIGS. 1 and 2, wherein the device 24 has been conformedas a letter W for display purposes.

In FIGS. 4 and is shown an alternative embodiment 26 for the device asshown in FIGS. 1 and 2, wherein an additional elongated, flexible andelectrically-conducting body 28 generally parallels the center coreportion 12. This additional conducting body 28 preferably has a crosssection which is considerably smaller than that of the center coresection 12 so that it will not absorb or block off any appreciableamount of light generated by the phosphor layer 14. The member 28 can bepositioned along the surface of the conducting layer 16 althoughpreferably it is embedded therein, as is shown in FIGS. 4 and 5. As anexample, the member 28 is fabricated of nickel-plated copper wire havinga diameter of 2 mils. The purpose of this additional conducting member28 is to serve as a bus bar for connection to the power supply so thatany tendencies for voltage drops through the layer 16 are minimized. Thedevice embodiment 26 is also modified from that embodiment shown inFIGS. 1 and 2 in that a layer of insulating and light-transmittingmaterial 30, such as a two-mil layer of polyvinyl-chloride acetate, iscarried over the conducting layer 16, in order to prevent shock hazard.Other than the indicated differences, the device embodiment 26 as shownin FIGS. 4 and 5 is similar to the device embodiment 19 shown in FIGS. 1and 2.

The device embodiments as shown in FIGS. 1 through 5 are subject toconsiderable variation. For example, the central core wire 12 as shownin FIG. 1 can be replaced by any :flexible electrically-conducting bodywhich is considerably elongated in comparison to its thickness andwidth. As an example, the wire 12 can be replaced by a copper tube.

In FIG. 6 is shown an electroluminescent device 32 which comprises twofiat, light-transmitting and vitreous foundation members 34, each ofwhich has one surface closely spaced from a corresponding surface of theother member. These closely spaced surfaces each carry thereon a thin,light-transmitting and electrically-conducting layer 36 of tin oxide.Other known electrode mate- Between the electrode layers 36 is includeda substantially-uniform-thick layer 38 comprising electroluminescentphosphor, which as an example is similar in thickness and composition tothe layer 14 as shown in FIG. 1, except that this layer 38 issubstantially planar. While the phosphor layer 38 can be provided with asubstantially uniform thickness, the tin-oxide-coated glass is subjectto some deviation from a planar configuration. If the phosphor orphosphor and dielectric are sandwiched directly between suchtin-oxide-coated lglass foundations, there will normally be somevariation in electrode spacing. In addition, it is difficult to maintaina constant average spacing between the electrode layers 36. Accordingly,when an alternating potential is applied between the electrodes of sucha device, there Will normally be some variations in the applied electricfield. Variations in the applied electric field will cause theelectroluminescent layer to respond with varying brightness. In order toeliminate such variable electric fields so that the device can emit asubstantially uniform light intensity from its opposite faces, at leastone layer of conducting solid material is also included between theelectrode layers. In fabricating such a device, either of the solidconducting materials as indicated hereinbefore is formed as a layer 40onto a tin oxide electrode layer 36. A heated gauge block is then placedover this layer of solid conducting material in order to cause thesurface portion thereof to melt to eliminate any surface irregularities.The phosphor-dielectric layer 38 is then sprayed over this firstappliedlayer 443 and such phosphor-dielectric layers can he sprayed to asubstantially uniform thickness of 2 mils for example. An additionallayer 40 of solid conducting material is then formed over the appliedphosphor-dielectric layer 38. The remaining vitreous foundation 34 isheated and the tin oxide coating thereon is pressed over thelast-applied conducting layer 40. With this construction, when apotential is applied between the tin oxide electrode layers 36, theresulting electric field will actually be applied between the solidconducting layers 40 and will be substantially uniform across thephosphor layer 38, even though the spacing between the tin oxideelectrode layers 36 varies.

In FIG. 7 is shown an alternative embodiment 42 for the deviceembodiment as shown in FIG. 6. The embodiment 42 essentially correspondsto the device as shown in FIG. 6 except that one of the con-ductingsolid layers 40 has been eliminated and an additional separate layer 44of light tr-ansmitting dielectric such as a plastic material has beenplaced between the phosphor-dielectric layer 38 and the remaining layer40. Such plastic layers are well known and as an example, the layer 44is formed of an acrylic resin having a thickness of 1 mil. The ad.-vantages to be realized from the device embodiment 42 are that the tinoxide electrodes 36 need not be maintained with a constant averagespacing therebetween, since the conducting layer 40 in effect serves asan electrode and can vary with respect to its thickness withoutintroducing electric field variations. In either of the embodiments asshown in FIGS. 6 and 7, each of the conducting layers 40 desirably hasan average thickness at least about as great as the phosphor layer 38 inorder to permit adequate tolerances in manufacturing with respect topositioning the vitreous foundations 34.

As a possible alternative construction for the embodiments as shown inFIGS. 6 and 7, the foundations can be formed of non-vitreous materialsuch as light-transmitting resins, an example being polystyrene. Inaddition, the electrode layers can be formed of a metal mesh embedded inthe surface of the polystyrene- With such a construction, the effect ofdiscontinuities in spacing between the metal mesh electrode layers willbe eliminated by the use of the light-transmitting, solid and conductinglayers as specified hereinbefore. The use of such solid, conductinglayers in conjunction with a metal mesh electrode layer also has utilityin conjunction with an electro-luminescent device such as is illustratedin FIG. 2 of U. S. Patent No. 2,765,419, dated October 2, 1956, whereina solid conducting layer as described hereinbefore can be placed betweenthe metal mesh electrode layer and the electro-luminescent phosphorlayer to form a planar electrode. In addition, the other electrode forsuch a device embodiment can be formed of opaque material, such asvacuum-metallized aluminum. Constructional details for such devices withrespect to the phosphor-dielectric layers and additional layers oflighttransmitting, solid and conducting materials can be specifiedhereinbefore.

The electroluminescent devices described hereinbefore are intended foroperation with alternating potential .excitation. Any of these devicescan be operated with D.C potential excitation if the amount ofdielectric material mixed with the phosphor is decreased a sufiicientamount so that the phosphor-dielectric layers will conduct D.C. As anexample, any of the foregoing embodiments will be operable under D.C.excitation if the phosphor con-- stitutes at least by weight of thephosphor-dielectnic layers.

It will be recognized that the objects of the invention have beenachieved by providing a flexible electroluminescent device which can beconformed to various shapes as well as an electroluminescent devicewhich emits a very uniform light intensity. There have also beenprovided constructional details for such flexible and uniform appearingdevices as Well as light-transmitting, flex-ible and conducting solidsubstance.

While best embodiments of the invention have been i1- lustrated anddescribed hereinbefore, it is to be particu larly understood that theinvention is not limited thereto or thereby.

We claim:

1. An electroluminescent device comprising, a first flexibleelectrically-conducting body considerably elongated in comparison to itsthickness and width, a flexible layer comprising electroluminescentphosphor over said first flexible elongated body, a flexiblelight-transmitting electrically-conducting and solid layer ofconsiderable thickness and at least principally comprising organiccompound over said layer comprising electroluminescent phosphor, anadditional elongated flexible and electricallyconducting body having across section considerably smaller than that of said first flexible bodyand electrically contacting throughout its length saidlight-transmitting conducting layer, and said first flexible elongatedbody and said additional conducting body adapted to have an alternatingpotential applied therebetween.

2. An electroluminescent device comprising, a first flexibleelectrically-conducting body considerably elongated in comparison to itsthickness and width, a flexible layer comprising electroluminescentphosphor over said flexible elongated body, a flexiblelight-transmitting electricallyconducting and solid layer ofconsiderable thickness and at least principally comprising organiccompound over said layer comprising electroluminescent phosphor, anadditional elongated flexible electrically-conducting body generallyparalleling said first conducting body and having a cross-sectionconsiderably smaller than that of said first conducting body, saidadditional conducting body embedded throughout substantially all itslength in said light-transmitting conducting layer, and said firstflexible elongated body and said additional conducting body adapted tohave an alternating potential applied therebetween.

3. An electroluminescent device comprising, a flexibleelectrically-conducting body considerably elongated in comparison to itsthickness and width, a flexible layer comprising electroluminescentphosphor over said flexible elongated body, a flexiblelight-transmitting electricallyconduoting and solid layer over saidlayer comprising electroluminescent phosphor, said flexible solid layerselected from one of the group consisting of succinonitrile and2,2-dinitropropane and having dissolved therein a predetermined amountof ionized salt to impart electrical conductivity thereto, and saidflexible elongated body and said conducting solid layer adapted to havean alternating potential applied therebetween.

4. An electroluminescent device comprising, two lighttransmittingfoundation members each having a surface closely spaced from a surfaceof the other member, a thin light transmitting andelectrically-conducting electrode layer carried on each of theclosely-spaced surfaces of said foundation member, asubstantially-uniform-thick layer comprising electroluminescent phosphorincluded between said spaced electrode layers, and at least onelight-transmitting said electrically-conducting solid layer at leastprincipally comprising organic compound also included between saidelectrode layers and having an average thickness at least about as greatas said layer comprising electroluminescent phosphor.

5. An electroluminescent device comprising, two lighttransmittingvitreous foundation members each having a surface closely spaced from asurface of the other member, a thin light-transmitting andelectrically-conducting electrode layer carried on each of theclosely-spaced surfaces of said foundation members, asubstantially-uniform-thick layer comprising electroluminescent phosphorincluded between said spaced electrode layers, an additional flexiblelight-transmitting and electrically-conducting solid layer at leastprincipally comprising organic compound also included between saidelectrode layers and having an average thickness at least about as greatas said phosphor layer, and an additional light-transmitting dielectriclayer included between said additional conducting layer and saidphosphor layer, whereby any deviations from a uniform average spacingbetween said electrode layers are compensated for by said additionalsolid conducting layer.

6. An electroluminescent device comprising, two lighttransmittingvitreous foundation members each having a surface closely spaced from acorresponding surface of the other member, a thin light-transmitting andelectrically-conducting electrode layer carried on each of theclosely-spaced surfaces of said foundation members, asubstantially-uniform-thick layer comprising electroluminescent phosphorincluded between said spaced electrode layers, at least one additionalflexible light-transmitting and electrically-conducting solid layer alsoincluded between said electrode layers and having an average thicknessat least about as great as said layer comprising electroluminescentphosphor, and said additional conducting layer selected from one of thegroup consisting of succinonitrile and 2,2-dinitropr0pane and havingdissolved therein a predetermined amount of ionized salt to impartelectrical conductivity thereto.

7. An electroluminescent device comprising, spaced electrodes, asubstantially-uniform-thick layer comprising electroluminescent phosphorbetween said spaced electrodes, and at least one layer of flexiblelight-transmitting and electrically-conducting materials at leastprincipally comprising organic compound also included between saidspaced electrodes.

8. An electroluminescent device comprising, spaced electrode layers, asubstantially-uniform-thick layer comprising electroluminescent phosphorbetween said spaced electrode layers, one of said electrode layers beinglight transmitting, a variable spacing between said one electrode layerand said phosphor layer, and a light-transmitting andelectrically-conducting solid layer at least principally comprisingorganic compound between said phosphor layer and said one electrodelayer.

9. An electroluminescent device comprising, spaced electrode layers, asubstantially-uniform-thick layer comprising electroluminescent phosphorbetween said spaced electrode layers, one of said electrode layers beinglight transmitting, a variable spacing between said one electrode layerand said phosphor layer, a flexible lighttransmitting andelectrically-conducting solid layer at least principally comprisingorganic compound between said phosphor layer and said one electrodelayer, and said flexible solid layer having an average thickness atleast about as great as the thickness of said phosphor layer.

10. A light-transmitting electrically-conducting solid substanceprincipally comprising material selected from the group consisting ofsuccinonitrile and 2,2-dinitropropane, and said material havingdissolved therein a predetermined amount of selected ionizable salt.

11. A flexible light-transmitting electrically-conducting solidsubstance principally comprising material selected from the groupconsisting of succinonitrile and 2,2-dinitropropane, and said materialhaving dissolved therein a predetermined amount of one of the groupconsisting of ammonium chloride, potassium bromide, ammonium acetate,trimethyl acetomethyl ammonium bromide and (CH NCl.

12. A flexible light-transmitting electrically-conducting solidsubstance principally comprising material selected from the groupconsisting of succinonitrile and References Cited in the file of thispatent UNITED STATES PATENTS Gillson Jan. 31, 1956 Payne June 10, 1958Kazan Sept. 9', 1958 Fridrich Aug. 25, 1959 Bartels Mar. 8, 1960Swindells June 14, 1960

1. AN ELECTROLUMINESCENT DEVICE COMPRISING, A FIRST FLEXIBLEELECTRICALLY-CONDUCTING BODY CONSIDERABLY ELONGATED IN COMPARISON TO ITSTHICKNESS AND WIDTH, A FLEXIBLE LAYER COMPRISING ELECTROLUMINESCENTPHOSPHOR OVER SAID FIRST FLEXIBLE ELONGATED BODY, A FLEXIBLELIGHT-TRANSMITTING ELECTRICALLY-CONDUCTING AND SOLID LAYER OFCONSIDERABLE THICKNESS AND AT LEAST PRINCIPALLY COMPRISING ORGANICCOMPOUND OVER SAID LAYER COMPRISING ELECTROLUMINESCENT PHOSPHOR, ANADDITIONAL ELONGATED FLEXIBLE AND ELECTRICALLYCONDUCTING BODY HAVING ACROSS SECTION CONSIDERABLY SMALLER THAN THAT OF SAID FIRST FLEXIBLE BODYAND ELECTRICALLY CONTACTING THROUGHOUT ITS LENGTH SAIDLIGHT-TRANSMITTING CONDUCTING LAYER, AND SAID FIRST FLEXIBLE ELONGATEDBODY AND SAID ADDITIONAL CONDUCTING BODY ADAPTED TO HAVE AN